Satan’s Slave (1976) is a British mildy erotic horror film, written by David McGillivray and directed by Norman J. Warren and starring Michael Gough.
A young girl, Catherine Yorke (Candace Glendenning), shares a ride with her parents to visit her uncle Alexander (Michael Gough), that no one had met before. But the drive ends in tragedy when Catherine’s parents die in a car accident.
The girl is then hosted by the mysterious Alexander, who lives in a beautiful house with his son Stephen (Martin Potter) and the faithful Frances (Barbara Kellerman). Catherine takes a taste for life and notices that Stephen is far from being insensitive to her charms. But Catherine is soon the victim of terrible hallucinations. As time passes on, Frances then informs her of what her uncle and cousin are planning to do to her. She tells them they plan to sacrifice her in order to avenge an ancient ancestor of hers named Camilla York (because the only way to resurrect the dead is through the body of a descendant) who was said to possess evil powers, she tells her that they plan to use Camilla’s powers for Alexander’s own evil.
Frances then offers to help her escape this terrible fate and run away from them. When Stephen finds out he kills Frances by slashing her with glass and stabbing her through her mouth. When Catherine discovers her dead body Stephen locks Catherine in her bedroom until the morning of the ritual. When they take her in the woods and prepare her, Catherine kills Stephen by stabbing him in the eye with a blade. She temporarily gets away then is tricked back into the clutches of her evil uncle by an illusion. When she is trapped by the cultists and the film ends on a neat suspense note.